Follow Up On Throttle Potentiometer Test...Could Someone Possibly Lend a Hand?

[pingu]

The Electrical Troubleshooting Manual (ETM) shows that pin 1 grounds one end of the resistance track of the pot. Pin 3 connects the other end of the resistance track to +5V.

Pin 2 connects to the wiper of the pot. I think the reason you're also getting +5V from pin 2 of the harness connector is that the DME internally has a pull-up on pin 2 (at least this is what the ETM shows) . The pull-up will normally be over-ridden by the wiper but if the pot isn't connected then the pull-up will weakly pull pin up to 5V (through a high value resistance).

If you've got nothing on pin 3 then the pot isn't getting +5V.

I don't think it's the DME relay as I presume that the whole DME is controlled by the relay - the throttle pot connects to the DME, not to the DME relay.

My money is on the DME connector or, more likely, the wiring is the problem. Come to think of it, you may have a partial break in the wire so that at it only connects when bent into a certain position. The fact that the problem occurs when accelerating/deaccelerating suggests that the engine movement is bending the wire slightly (though this could be a red herring). Try bypassing pin 3 directly to the DME (I know this is easier said than done...) ?

[Dave M]

The Electrical Troubleshooting Manual (ETM) shows that pin 1 grounds one end of the resistance track of the pot. Pin 3 connects the other end of the resistance track to +5V.

Pin 2 connects to the wiper of the pot. I think the reason you're also getting +5V from pin 2 of the harness connector is that the DME internally has a pull-up on pin 2 (at least this is what the ETM shows) . The pull-up will normally be over-ridden by the wiper but if the pot isn't connected then the pull-up will weakly pull pin up to 5V (through a high value resistance).

If you've got nothing on pin 3 then the pot isn't getting +5V.

I don't think it's the DME relay as I presume that the whole DME is controlled by the relay - the throttle pot connects to the DME, not to the DME relay.

My money is on the DME connector or, more likely, the wiring is the problem. Come to think of it, you may have a partial break in the wire so that at it only connects when bent into a certain position. The fact that the problem occurs when accelerating/deaccelerating suggests that the engine movement is bending the wire slightly (though this could be a red herring). Try bypassing pin 3 directly to the DME (I know this is easier said than done...) ?

Funny you should reply now, as I just got back from a drive and did some investigating. As i said, the stuttering is primarily limited to the engine warm up period. Once its warm and been driven for ~ 1/2 hour, I almost never get any symptoms. I think its more temp related than anything else.

So, I pulled into the garage after driving under all conditions, loads, engine speads etc. attempting to cause the stutter. As i'd been driving it for a while, it was solid, no probs. I popped the hood, pulled off the harness and tested terminals 2 and 3 again. Low and behold, now i have 5V to both.

Coincedence? I'm guessing, as you are, that somewhere (preferably at the harness) there is a bad connection. I am going to test it again in the morning when its cold to confirm no voltage at #3. I'll then drive it until the stuttering stops and test it again for voltage. Once confirmed I'll clean the harness and pot with contact cleaner (thanks Ryan) and try again. If that doesn't work I'll check into the wiring.

Thanks again for all your help. I'll report back,

Dave M

[Blitzkrieg Bob]

Maybe when you swapped motors something got pinched.

I've done it while lowering motors and trans into place ..bellhousing bumps the harness and pinches a wire.

This must be driving you nutz

[ryan roopnarine]

was going to suggest earlier that you use the contact cleaner on the tps terminals, and, if you felt brave enough, to try it on the DME terminals and wire harness terminals. some people can break things with contact cleaner, somehow....didn't want you to get stranded without a dme. it would be pretty easy for you to go over the terminals with contact cleaner since it would appear that things are going in that direction, and might solve your problem. the e-box is pretty close to the engine, and heat/vibration might be making stuff work intermittently.

[Dave M]

Maybe when you swapped motors something got pinched.

I've done it while lowering motors and trans into place ..bellhousing bumps the harness and pinches a wire.

This must be driving you nutz

Well, its a bit annoying when it studders in traffic, but I've got two other junkers to fall back on if gets too bad, and the e34 is going to bed in the month anyway. In all truth, I haven't spent a dime (except for the contact cleaner) and i'm learning a bit about electrical crap, which is something I've needed to do for a looooong time.

We'll fix it

Dave M